The currently observed architectures of extrasolar planetary systems trace the processes of planetary formation and evolution. Until recently, Jovian-size planets provided nearly all of the observational constraints. From Doppler studies, we detect a steeply rising planet mass distribution down to at least 3 Earth-masses for planets orbiting inside of 0.25 AU. The planet size distribution from Kepler also shows a steep rise with decreasing size, but with a plateau in the occurrence rate for 1{2.8 times Earth size. Analyses of the Kepler data support the bottom-up picture of planet formation by core accretion.

Multiple different groups have generated a wide variety of mission concepts for direct exoplanet imaging, incorporating a variety of spacecraft architectures and starlight suppression systems. Here, we present a framework for modeling exoplanet surveys based on these concepts, including systematic methods for predicting their expected science yields, thereby allowing for the direct comparison of different mission concepts. We describe in detail the components of this modeling framework and demonstrate how we can generate simulated planetary populations that are broadly consistent with the results of the Kepler transit survey and previous radial velocity surveys. We present results of end-to-end mission simulations, focusing in particular on the 2.4 m aperture scale provided by the Astrophysics Focused Telescope Asset and set top level requirements for the coronagraph needed to discover and characterize new planets with this telescope.

Kepler vaulted into the heavens on March 7, 2009, initiating NASA’s search for Earth-size planets orbiting Sun-like stars
in the habitable zone, where liquid water could exist on the planetary surface and support alien biology. Never before has
there been a photometer capable of reaching a precision near 20 ppm in 6.5 hours while conducting nearly continuous
and uninterrupted observations for several years. The flood of exquisite photometric data over the last 4 years on
190,000+ stars has provoked a watershed of results. Over 2,700+ candidate planets have been identified of which an
astounding 1171 orbit 467 stars. Over 120+ planets have confirmed or validated and the data have also led to a
resounding revolution in asteroseismology. Recent discoveries include Kepler-62 with 5 planets total of which 2 are in
the habitable zone, and are 1.4 and 1.7 times the radius of the Earth. Designing and building the Kepler photometer and
the software systems that process and analyze the resulting data presented a daunting set of challenges, including how to
manage the large data volume, how to detect miniscule transit signatures against stellar variability and instrumental
effects, and how to review hundreds of diagnostics produced for each of ~20,000 candidate transit signatures. The
challenges continue into flight operations, as the photometer and spacecraft have experienced aging and changes in
hardware performance over the course of time. The success of Kepler sets the stage for TESS, NASA’s next mission to
detect Earth’s closest cousins.

Combining high-contrast imaging and astrometry in a single space mission would enable efficient detection and characterization of single- and multiple- planetary systems around nearby stars, allowing determination of planetary mass, composition, atmosphere, and system architecture. These science goals can be achieved using a 2m wide-field (>0.1deg2) class telescope equipped with two instruments: a high-performance coronagraph to perform direct imaging, and a wide field camera to achieve sub-microarcsecond astrometric accuracy. However, these measurements are only possible if there are no relative distortion changes between astrometric observations. At sub-microarcsecond accuracy regime, even space optics suffers from dynamic distortions in the optical system and dominates the error budget. We propose to utilize a diffractive pupil, in which an array of dots on the primary mirror generates polychromatic diffraction spikes in the focal plane to calibrate the dynamic distortions of the optical system. According to simulations, this technique would allow to obtain 0.2microarcsecond single-visit precision astrometric accuracy. In this paper we present the laboratory results that demonstrate the diffractive pupil concept on wide-field images. We also discuss simulations and experiments performed at the NASA Ames ACE test bed, demonstrating that the diffractive pupil does not affect the coronagraph performance down to 2x10-7. Finally, we assess the compatibility of a diffractive pupil telescope with a general astrophysics mission, showing that the spikes do not impact wide-field observations.

We review the progress on the New Worlds Airship project, which has the eventual goal of suborbitally mapping the Alpha Centauri planetary system into the Habitable Zone. This project consists of a telescope viewing a star that is occulted by a starshade suspended from an airship. The starshade suppresses the starlight such that fainter planetary objects near the star are revealed. A visual sensor is used to determine the position of the starshade and keep the telescope within the starshade’s shadow. In the first attempt to demonstrate starshades through astronomical observations, we have built a precision line of sight position indicator and flew it on a Zeppelin in October (2012). Since the airship provider went out of business we have been redesigning the project to use Vertical Takeoff Vertical Landing rockets instead. These Suborbital Reusable Launch Vehicles will serve as a starshade platform and test bed for further development of the visual sensor. We have completed ground tests of starshades on dry lakebeds and have shown excellent contrast. We are now attempting to use starshades on hilltops to occult stars and perform high contrast imaging of outer planetary systems such as the debris disk around Fomalhaut.

EChO is an M-class mission candidate within the science program Cosmic Vision 2015-2025 of the European Space Agency. It aims at characterising the atmosphere of known transiting exoplanets, potentially from giant Hot Jupiters down to Super-Earths orbiting in the habitable zone of M-dwarf stars.

It was selected in February 2011 to enter an assessment phase (phase 0/A). Following the completion of the Concurrent Design Facility study conducted by ESA in June/July 2011, two parallel industrial studies were carried out throughout 2012, and were then extended till August 2013. Similarly, two parallel instrument studies were conducted till mid-2012, following which an Announcement of Opportunity was released and concluded in February 2013 by the selection of a single instrument consortium.

This paper describes the status of EChO upon completion of the system level and instrument studies. It includes a discussion on the evolution of the science and mission requirements, the description of the final preliminary design and performance parameters, as well as programmatic estimates in terms of technology readiness and schedule.

The next step for EChO will consist of passing the Preliminary Requirements Review, planned by the end of 2013, followed by the down-selection of a single M3 mission.

The Debris Disk Explorer (DDX) is a proposed balloon-borne investigation of debris disks around nearby stars. Debris disks are analogs of the Asteroid Belt (mainly rocky) and Kuiper Belt (mainly icy) in our Solar System. DDX will measure the size, shape, brightness, and color of tens of disks. These measurements will enable us to place the Solar System in context. By imaging debris disks around nearby stars, DDX will reveal the presence of perturbing planets via their influence on disk structure, and explore the physics and history of debris disks by characterizing the size and composition of disk dust. The DDX instrument is a 0.75-m diameter off-axis telescope and a coronagraph carried by a stratospheric balloon. DDX will take high-resolution, multi-wavelength images of the debris disks around tens of nearby stars. Two flights are planned; an overnight test flight within the United States followed by a month-long science flight launched from New Zealand. The long flight will fully explore the set of known debris disks accessible only to DDX. It will achieve a raw contrast of 10−7, with a processed contrast of 10−8. A technology benefit of DDX is that operation in the near-space environment will raise the Technology Readiness Level of internal coronagraphs, deformable mirrors, and wavefront sensing and control, all potentially needed for a future space-based telescope for high-contrast exoplanet imaging.

Direct imaging of exoplanet is one of the most exciting field of planetology today. The light coming from exoplanet orbiting their host star witnesses for the chemical composition of the atmosphere, and the potential biomarkers for life. However, the faint flux to be imaged, very close to the huge flux of the parent star, makes this kind of observation extremely difficult to perform from the ground. The direct imaging instruments (SPHERE [1], GPI [2]) are nowaday reaching lab maturity. Such instrument imply the coordination of XAO for atmospherical turbulence real-time correction, coronagraphy for star light extinction, IR Dual band camera, IFS, and visible polarimetry. The imaging modes include single and double difference (spectral and angular). The SPHERE project is now at the end of AIT phase. This paper presents the very last results obtained in laboratory, with realistic working conditions. These AIT results allows one to predict on-sky performance, that should come within the next weeks after re-installation at Very Large Telescope at Paranal.

SPHERE (Spectro-Polarimetric High Contrast Exoplanet Research) is one of the first instruments which aim for the direct detection from extra-solar planets. SPHERE commissioning is foreseen in 2013 on the VLT. ZIMPOL (Zurich Imaging Polarimeter) is the high contrast imaging polarimeter subsystem of the ESO SPHERE instrument. ZIMPOL is dedicated to detect the very faint reflected and hence polarized visible light (600-900 nm) from extrasolar planets. It is located behind an extreme AO system (SAXO) and a stellar coronagraph. We present the first high contrast polarimetric results obtained for the fully integrated SPHERE-ZIMPOL system. We have measured the polarimetric high contrast performance of several coronagraphs: a Classical Lyot on substrate, a suspended Classical Lyot and two 4 Quadrant Phase Mask coronagraphs. We describe the impact of crucial system parameters – Adaptive Optics, Coronagraphy and Polarimetry - on the contrast performance.

The final performance of current and future instruments dedicated to exoplanet detection and characterization (such as SPHERE on the VLT, GPI on Gemini North or future instruments on the E-ELT) is limited by intensity residuals in the scientific image plane, which originate in uncorrected optical aberrations. After correction of the atmospheric turbulence, the main contribution to these residuals comes from the quasi-static aberrations introduced upstream of the coronagraph. In order to measure and compensate for these aberrations, we propose a dedicated focal-plane sensor called COFFEE (for COronagraphic Focal-plane wave-Front Estimation for Exoplanet detection), which consists in an extension of conventional phase diversity to a coronagraphic system: aberrations both upstream and downstream of the coronagraph are estimated using two coronagraphic focal-plane images, recorded from the scientific camera itself, without any differential aberration. This communication gathers COFFEE’s improvements: the phase estimation is performed on a pixel-wise map coupled with a dedicated regularization metric. This allows COFFEE to estimate very high order aberrations, making possible to estimate and compensate for quasi-static aberrations with nanometric precision, leading to an optimization of the contrast on the scientific detector in the whole AO corrected area. Besides, COFFEE has been modified so that it can be used with any coronagraphic focal plane mask. Lastly, we use COFFEE to measure and correct the wavefront on the SPHERE (Spectro-Polarimetric High-contrast Exoplanet Research) instrument during its integration phase: COFFEE’s estimation is used to compensate for the quasi-static aberrations upstream of the coronagraph, leading to a contrast improvement on the scientific camera.

ESPRESSO is the next European exoplanets hunter. It will combine the efficiency of modern echelle spectrograph with extreme radial-velocity precision. It will be installed at Paranal's VLT in order to achieve two magnitudes gain with respect to its predecessor HARPS, and the instrumental radial-velocity precision will be improved to reach 10 cm/s level. We have constituted a Consortium of astronomical research institutes to fund, design and build ESPRESSO on behalf of and in collaboration with ESO, the European Southern Observatory. The project has passed the final design review in May 2013. The spectrograph will be installed at the Combined Coudé Laboratory of the VLT, it will be linked to the four 8.2 meters Unit Telescopes through four optical "Coudé trains" and will be operated either with a single telescope or with up to four UTs, enabling an additional 1.5 magnitude gain. Thanks to its characteristics and ability of combining incoherently the light of 4 large telescopes, ESPRESSO will offer new possibilities in many fields of astronomy. Our main scientific objectives are, however, the search and characterization of rocky exoplanets in the habitable zone of quiet, near-by G to M-dwarfs, and the analysis of the variability of fundamental physical constants. In this paper, we will present the scientific objectives, the capabilities of ESPRESSO, the technical solutions for the system and its subsystems, enlightening the main differences between ESPRESSO and its predecessors. The project aspects of this facility are also described, from the consortium and partnership structure to the planning phases and milestones.

This paper presents the Espresso Exposure Meter (EM) implementation. ESPRESSO,1-3 the Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations, will be installed on ESOs Very Large Telescope (VLT). The light coming from the Telescope through a Coud Focus4 of all the Four Telescope Units (UTs) will be collected by the Front End Unit that provides Field and Pupil stabilisation and injects the beams into the Spectrograph fibers.5 An advanced Exposure Meter system will be used to correct Radial Velocity (RV) obtained from the scientific spectrum for the Earth relative motion. In this work we will present the perfor mance of an innovative concept for the Exposure Meter system based on a Charge Coupled Device (CCD) with a chromatic approach for the calculation of the Mean Time of Exposure (MTE). The MTE is a crucial quantity used for the correction of RV for the Earth relative motion during the exposure. In particular, splitting the light in different chromatic channels on the CCD, we will probe for potential chromatic effects on the calculation of the MTE in each channel and how they could be used in order to perform the correction of RV. The paper is accompanied by a fully described numerical analysis that keeps into view a key performance evaluation for different stellar spectral types (B to M spectral main sequence classes).

We have built and commissioned a prototype agitated non-circular core ber scrambler for precision spectroscopic radial velocity measurements in the near-infrared H band. We have collected the rst on-sky performance and modal noise tests of these novel bers in the near-infrared at H and K bands using the CSHELL spectrograph at the NASA InfraRed Telescope Facility (IRTF). We discuss the design behind our novel reverse injection of a red laser for co-alignment of star-light with the ber tip via a corneWe have built and commissioned a prototype agitated non-circular core fiber scrambler for precision spectroscopic radial velocity measurements in the near-infrared H band. We have collected the first on-sky performance and modal noise tests of these novel fibers in the near-infrared at H and K bands using the CSHELL spectrograph at the NASA InfraRed Telescope Facility (IRTF). We discuss the design behind our novel reverse injection of a red laser for co-alignment of star-light with the fiber tip via a corner cube and visible camera. We summarize the practical details involved in the construction of the fiber scrambler, and the mechanical agitation of the fiber at the telescope. We present radial velocity measurements of a bright standard star taken with and without the fiber scrambler to quantify the relative improvement in the obtainable blaze function stability, the line spread function stability, and the resulting radial velocity precision. We assess the feasibility of applying this illumination stabilization technique to the next generation of near-infrared spectrographs such as iSHELL on IRTF and an upgraded NIRSPEC at Keck. Our results may also be applied in the visible for smaller core diameter fibers where Fiber modal noise is a significant factor, such as behind an adaptive optics system or on a small < 1 meter class telescope such as is being pursued by the MINERVA and LCOGT collaborations.r cube and visible camera. We summarize the practical details involved in the construction of the ber scrambler, and the mechanical agitation of the ber at the telescope. We present radial velocity measurements of a bright standard star taken with and without the ber scrambler to quantify the relative improvement in the obtainable blaze function stability, the line spread function stability, and the resulting radial velocity precision. We assess the feasibility of applying this illumination stabilization technique to the next generation of near-infrared spectrographs such as iSHELL on IRTF and an upgraded NIRSPEC at Keck. Our results may also be applied in the visible for smaller core diameter bers where ber modal noise is a signi cant factor, such as behind an adaptive optics system or on a small < 1 meter class telescope such as is being pursued by the MINERVA and LCOGT collaborations.

Princeton University is building an integral field spectrograph (IFS), the Coronagraphic High Angular Resolution Imaging Spectrograph (CHARIS), for integration with the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system and the AO188 adaptive optics system on the Subaru telescope. CHARIS and SCExAO will measure spectra of hot, young Jovian planets in a coronagraphic image across J, H, and K bands down to an 80 milliarcsecond inner working angle. SCExAO’s coronagraphs and wavefront control system will make it possible to detect companions five orders of magnitude dimmer than their parent star. However, quasi-static speckles in the image contaminate the signal from the planet. In an IFS this also causes uncertainty in the spectra due to diffractive cross-contamination, commonly referred to as crosstalk. Post-processing techniques can subtract these speckles, but they can potentially skew spectral measurements, become less effective at small angular separation, and at best can only reduce the crosstalk down to the photon noise limit of the contaminating signal. CHARIS will address crosstalk effects of a high contrast image through hardware design, which drives the optical and mechanical design of the assembly. The work presented here sheds light on the optical and mechanical considerations taken in designing the IFS to provide high signal-to-noise spectra in a coronagraphic image from and extreme adaptive optics image. The design considerations and lessons learned are directly applicable to future exoplanet instrumentation for extremely large telescopes and space observatories capable of detecting rocky planets in the habitable zone.

In November 2012, we installed an L-band annular groove phase mask (AGPM) vector vortex coronagraph (VVC) inside NACO, the adaptive optics camera of ESO’s Very Large Telescope. The mask, made out of diamond subwavelength gratings has been commissioned, science qualified, and is now offered to the community. Here we report ground-breaking on-sky performance levels in terms of contrast, inner working angle, and discovery space. This new practical demonstration of the VVC, coming a few years after Palomar’s and recent record-breaking lab experiments in the visible (E. Serabyn et al. 2013, these proceedings), shows once again that this new-generation coronagraph has reached a high level of maturity.

We present a new Adaptive Phase Mask (APM) coronagraph design enabling Amplitude and Phase Modulation control (APM). The Adaptive Phase mask coronagraph is a technique proposed to provide both high dynamic and high angular resolution imaging of faint sources around bright objects. Discriminating faint sources from static speckles is a challenging problem. Our new system is based on synchronous demodulation that allows high dynamic range detection of a faint target immersed in a background. The APM2 uses the coherence of speckles to discriminate them from proper companions, using the mask itself as the electric field modulator. Synchronous detection in the radio frequency range is used to side-step the effect of atmospheric turbulence and enable the detection of low amplitude signals. The APM2 concept offers high dynamic range detection and provides a time- and cost-effective method to quantify the probability of presence of a faint object close to the central star.

The Project 1640 instrument on the 200-inch Hale telescope at Palomar Observatory is a coronagraphic instru- ment with an integral eld spectrograph at the back end, designed to nd young, self-luminous planets around nearby stars. To reach the necessary contrast for this, the PALM-3000 adaptive optics system corrects for fast atmospheric speckles, while CAL, a phase-shifting interferometer in a Mach-Zehnder con guration, measures the quasistatic components of the complex electric eld in the pupil plane following the coronagraphic stop. Two additional sensors measure and control low-order modes. These eld measurements may then be combined with a system model and data taken separately using a white-light source internal to the AO system to correct for both phase and amplitude aberrations. Here, we discuss and demonstrate the procedure to maintain a half-plane dark hole in the image plane while the spectrograph is taking data, including initial on-sky performance.

P1640 high contrast imaging system on the Palomar 200 inch Telescope consists of an apodized-pupil Lyot coronagraph, the PALM-3000 adaptive optics (P3K-AO), and P1640 Calibrator (CAL). Science images are recorded by an integral field spectrograph covering J-H bands for detecting and characterizing stellar companions. With aberrations from atmosphere corrected by the P3K-AO, instrument performance is limited mainly by the quasi-static speckles due to noncommon path wavefront aberrations for the light to propagate to the P3K-AO wavefront sensor and to the coronagraph mask. The non-common path wavefront aberrations are sensed by CAL, which measures the post-coronagraph E-field using interferometry, and can be effectively corrected by offsetting the P3K-AO deformable mirror target position accordingly. Previously, we have demonstrated using CAL measurements to correct high order wavefront aberrations, which is directly connected to the static speckles in the image plane. Low order wavefront, on the other hand, usually of larger amplitudes, causes light to leak through the coronagraph making the whole image plane brighter. Knowledge error in low order wavefront aberrations can also affect the estimation of the high order wavefront. Even though, CAL is designed to sense efficiently high order wavefront aberrations, the low order wavefront front can be inferred with less sensitivity. Here, we describe our method for estimating both low and high order wavefront aberrations using CAL measurements by propagating the post-coronagraph E-field to a pupil before the coronagraph. We present the results from applying this method to both simulated and experiment data.

Direct imaging of exoplanets is very challenging because the planet is 104 to 1010 fainter than the star at a separation of a fraction of arcsec. Several coronagraphs have been proposed to reduce the contrast ratio but their performance strongly depends on the level of phase and amplitude aberrations that induce speckles in the science image. An active control of the aberrations and a posteriori calibration are thus required to reach very high contrasts. Classical adaptive optics are not sufficient for this purpose because of non-common path aberrations. Our team proposed a self-coherent camera that spatially modulates the speckles in the science image. It is then possible to both actively control a deformable mirror and calibrate the residuals a posteriori. The current paper is an overview of the developments we have been working on for 7 years. We present the principle of the self-coherent camera, laboratory performance obtained in monochromatic light, and upgrades of the technique to make it achromatic.

Direct detection is a very promising field in exoplanet science. It allows the detection of companions with large separation and allows their spectral analysis. A few planets have already been detected and are under spectral analysis. But the full spectral characterization of smaller and colder planets requires higher contrast levels over large spectral bandwidths. Coronagraphs can be used to reach these contrasts, but their efficiency is limited by wavefront aberrations. These deformations induce speckles, star lights leaks, in the focal plane after the coronagraph. The wavefront aberrations should be estimated directly in the science image to avoid usual limitations by differential aberrations in classical adaptive optics. In this context, we introduce the Self- Coherent Camera (SCC). The SCC uses the coherence of the star light to produce a spatial modulation of the speckles in the focal plane and estimate the associated electric complex field. Controlling the wavefront with a deformable mirror, high contrasts have already been reached in monochromatic light with this technique. The performance of the current version of the SCC is limited when widening the spectral bandwidth. We will present a theoretical analysis of these issues and their possible solution. Finally, we will present test bench performance in polychromatic light.

The mission EXCEDE (EXoplanetary Circumstellar Environments and Disk Explorer), selected by NASA for technology development, is designed to study the formation, evolution and architectures of exoplanetary systems and characterize circumstellar environments into stellar habitable zones. It is composed of a 0.7 m telescope equipped with a Phase-Induced Amplitude Apodization Coronagraph (PIAA-C) and a 2000-element MEMS deformable mirror, capable of raw contrasts of 10−6 at 1.2 λ/D and 10−7 above 2 λ/D. One of the key challenges to achieve those contrasts is to remove low-order aberrations, using a Low-Order WaveFront Sensor (LOWFS). An experiment simulating the starlight suppression system is currently developed at NASA Ames Research Center, and includes a LOWFS controlling tip/tilt modes in real time at 500 Hz. The LOWFS allowed us to reduce the tip/tilt disturbances to 10−3 λ/D rms, enhancing the previous contrast by a decade, to 8×10−7 between 1.2 and 2 λ/D. A Linear Quadratic Gaussian (LQG) controller is currently implemented to improve even more that result by reducing residual vibrations. This testbed shows that a good knowledge of the low-order disturbances is a key asset for high contrast imaging, whether for real-time control or for post processing.

As part of the NASA ROSES Technology Demonstrations for Exoplanet Missions (TDEM) program, we conducted a numerical modeling study of three internal coronagraphs (PIAA, vector vortex, hybrid bandlimited) to understand their behaviors in realistically-aberrated systems with wavefront control (deformable mirrors). This investigation consisted of two milestones: (1) develop wavefront propagation codes appropriate for each coronagraph that are accurate to 1% or better (compared to a reference algorithm) but are also time and memory efficient, and (2) use these codes to determine the wavefront control limits of each architecture. We discuss here how the milestones were met and identify some of the behaviors particular to each coronagraph. The codes developed in this study are being made available for community use. We discuss here results for the HBLC and VVC systems, with PIAA having been discussed in a previous proceeding.

Using NASA’s High Contrast Imaging Testbed (HCIT) at the Jet Propulsion Laboratory, we have experimentally investigated the sensitivity of dark hole contrast in a Lyot coronagraph for the following factors: 1) Lateral and longitudinal translation of an occulting mask; 2) An opaque spot on the occulting mask; 3) Sizes of the controlled dark hole area. Also, we compared the measured results with simulations obtained using both MACOS (Modeling and Analysis for Controlled Optical Systems) and PROPER optical analysis programs with full three-dimensional near-field diffraction analysis to model HCIT’s optical train and coronagraph.

We present coronagraphic images from the Phase Induced Amplitude Apodization (PIAA) coronagraph on NASA's High Contrast Imaging Testbed (HCIT) at the Jet Propulsion Lab, showing contrasts of 5×10−10 averaged from 2-4 λ/D, in monochromatic light at 808 nm. In parallel with the coronagraph and its deformable mirror and coronagraphic wavefront control, we also demonstrate a low-order wavefront control system, giving 100× rms suppression of introduced tip/tilt disturbances down to residual levels of 10−3 λ/D. Current limitations, as well as broadband (10% fractional bandpass) preliminary results are discussed.

Quasi-static speckles are one of the main limitations in imaging exoplanets, since the image of a planet looks similar to a speckle. However, speckles are light from the same coherent source, the star, and incoherent with the planet. By moving the deformable mirror after each image, the speckle pattern as seen on the camera changes between images. The change is very small within the full width half max of the planet, so changes in the planet image are minimal. This fundamental coherence property of the speckles (and incoherence with the planet light) guides us to develop a planet detection method to distinguish a planet from a speckle by taking advantage of a changing speckle pattern. We present a planet detection algorithm using a Bayesian analysis. We seek to conduct a hypothesis test at each pixel in the image to detect the presence of a planet at that location. We formulate a test statistic and use a least-squares method to estimate the unknown parameters. These parameters are the intensities of a planet and a locally constant background. Our algorithm assumes the speckle pattern is independent from one image to another. This approach is used to formulate an integration time estimate for detection of a planet with specified probabilities of false alarms and missed detections. A comparison is made between a single stacked image and using multiple images.

The High Contrast Imaging Laboratory (HCIL) at Princeton has developed several important algorithms and technologies for space-based coronagraphy missions to detect earth-like exoplanets. Before June 2013 the HCIL was the only facility with two deformable mirrors (DMs) in series for focal plane wavefront control, which allows for quasi-static speckle correction on both sides of the image plane. From June through August 2013, the High- Contrast Imaging Testbed (HCIT) at JPL had a second DM installed. In this paper we report on the results of our Technology Development for Exoplanet Missions project to achieve high contrast in two symmetric dark holes using a shaped pupil (SP) coronagraph at the HCIT. Our previous experiment with a similar SP at the HCIT in 2007 yielded single-sided dark holes. That experiment utilized an iterative, batch-process wavefront estimator and Electric Field Conjugation for wavefront control. Our current tests use the faster Kalman filter estimator and the stroke minimization control algorithm. We use the same ripple-style SPs as in the previous HCIT experiment because that mask manufacturing technique proved successful. Our tests of symmetric dark holes in monochromatic light at the HCIT demonstrate Princeton’s steady improvements in wavefront control and estimation techniques for a space-based coronagraphy mission.

To meet the high contrast requirement of 1 × 10−10to image an Earth-like planet around a Sun-like star, space telescopes equipped with coronagraphs require wavefront control systems. Deformable mirrors are a key element of these systems that correct for optical imperfections, thermal distortions, and diffraction that would otherwise corrupt the wavefront and ruin the contrast. However, high-actuator-count MEMS deformable mirrors have yet to fly in space long enough to characterize their on-orbit performance and reduce risk by developing and operating their supporting systems. The goal of the MEMS Deformable Mirror CubeSat Testbed is to develop a CubeSat-scale demonstration of MEMS deformable mirror and wavefront sensing technology. In this paper, we consider two approaches for a MEMS deformable mirror technology demonstration payload that will fit within the mass, power, and volume constraints of a CubeSat: 1) a Michelson interferometer and 2) a Shack-Hartmann wavefront sensor. We clarify the constraints on the payload based on the resources required for supporting CubeSat subsystems drawn from subsystems that we have developed for a different CubeSat flight project. We discuss results from payload lab prototypes and their utility in defining mission requirements.

An innovative integrated spatial filter array (iSFA) was developed for the nulling interferometer for the detection of earth-like planets and life beyond our solar system. The coherent iSFA comprised a 2D planar lightwave circuit (PLC) array coupled with a pair of 2D lenslet arrays in a hexagonal grid to achieve the optimum fill factor and throughput. The silica-on-silicon waveguide mode field diameter and numerical aperture (NA) were designed to match with the Airy disc and NA of the microlens for optimum coupling. The lenslet array was coated with a chromium pinhole array at the focal plane to pass the single-mode waveguide but attenuate the higher modes. We assembled a 32 by 30 array by stacking 32 chips that were produced by photolithography from a 6-in. silicon wafer. Each chip has 30 planar waveguides. The PLC array is inherently polarization-maintaining (PM) and requires much less alignment in contrast to a fiber array, where each PM fiber must be placed individually and oriented correctly. The PLC array offers better scalability than the fiber bundle array for large arrays of over 1,000 waveguides.

Coronagraph technology is advancing and promises to enable space telescopes capable of directly detecting low surface brightness circumstellar debris disks as well as giant planets as close as in the habitable zones of their host stars. One mission capable of doing this is called EXCEDE (EXoplanetary Circumstellar Environments and Disk Explorer), which in 2011 was selected by NASA's Explorer program for technology development (Category III). EXCEDE is a 0.7m space telescope concept designed to achieve raw contrasts of 10-6 at an inner working angle of 1.2 λ/D and 10-7 at 2 λ/D and beyond. In addition to doing fundamental science on debris disks, EXCEDE will also serve as a technological and scientific precursor for an exo-Earth imaging mission. EXCEDE uses a Starlight Suppression System (SSS) based on the Phase Induced Amplitude Apodization (PIAA) coronagraph to provide high throughput and high contrast close to the diffraction limit, enabling aggressive performance. We report on our continuing progress of developing the SSS for EXCEDE, including (a) high contrast performance demonstrations at 1.2 λD, which includes a lab demonstration of 2x10-7 median contrast between 1.2 and 2.0 λ/D simultaneously with 6.5x10-8 median contrast between 2 and 4 λ/D in monochromatic light at 655nm, meeting a major milestone in our technology development program; (b) the installation of a new Low Order Wavefront Sensor (LOWFS) which enabled achieving deep contrasts at aggressive inner working angles; (c) implementation of more efficient model-based wavefront control algorithms; and (d) a preliminary broadband contrast result of 6x10-6 contrast at 1.2 λ/D in a 10% band.

The detection of extrasolar planets, using both space- and ground-based telescopes, is one of the most exciting fields in astronomy today, with the ultimate goal of the direct direction of earth-like planets in the habitable zone. It is with this vision that the explorer mission EXCEDE selected by NASA for technology development, is designed. EXCEDE (Exoplanetary Circumstellar Environment and Disk Explorer) is composed of a 0.7 m telescope equipped with a Phase-Induced Amplitude Apodization Coronagraph (PIAA-C) and a 2000-element MEMS deformable mirror, capable of raw contrasts of 10-6 at 1.2 λ/D and 10-7 above 2 λ/D. Obtaining these contrasts requires precise wavefront control algorithms used in conjuncture with deformable mirrors. Unlike other optical systems, where the goal is to obtain the best wavefront, we aim at canceling the diffracted light coming from the parent star in a specific region to increase signal-to-noise of the planet. To do so, we use wavefront control techniques, such as Electric Field Conjugation (EFC) and speckle nulling, already developed and soon to be operational on 8-m class telescopes. One caveat is that the demonstration was done at moderate separations (r> 3λ/D).In this paper, we present tricks and techniques to perform high-contrast imaging at 1.2 λ/d using the NASA Ames Coronagraph Experiment testbed.

The vortex coronagraph has already enabled high-contrast observations very close to bright stars on large ground-based telescopes, and it also has great potential for use on coronagraphic space missions aimed at exoplanet detection and characterization. As such, demonstrations of vortex coronagraph performance have recently been carried out in JPL’s High Contrast Imaging Testbed. Some of our recent results are presented here, including the suppression of a monochromatic, single-polarization point-source to below the 10-9 level over a dark hole covering both the 2-7 λ/D and 3-8 λ/D regions, as well as the suppression of a 10% band of white-light to approximately the 10-8 level over a 3-8 λ/D dark hole.

We present a new method to achieve high-contrast images using segmented and/or on-axis telescopes. Our approach relies on using two sequential Deformable Mirrors to compensate for the large amplitude excursions in the telescope aperture due to secondary support structures and/or segment gaps. In this configuration the parameter landscape of Deformable Mirror Surfaces that yield high contrast Point Spread Functions is not linear, and non-linear methods are needed to find the true minimum in the optimization topology. We solve the highly non-linear Monge-Ampere equation that is the fundamental equation describing the physics of phase induced amplitude modulation. We determine the optimum configuration for our two sequential Deformable Mirror system and show that high-throughput and high contrast solutions can be achieved using realistic surface deformations that are accessible using existing technologies. We name this process Active Compensation of Aperture Discontinuities (ACAD). We show that for geometries similar to JWST, ACAD can attain at least 10-7 in contrast and an order of magnitude higher for future Extremely Large Telescopes, even when the pupil features a missing segment" . We show that the converging non-linear mappings resulting from our Deformable Mirror shapes actually damp near-field diffraction artifacts in the vicinity of the discontinuities. Thus ACAD actually lowers the chromatic ringing due to diffraction by segment gaps and strut's while not amplifying the diffraction at the aperture edges beyond the Fresnel regime and illustrate the broadband properties of ACAD in the case of the pupil configuration corresponding to the Astrophysics Focused Telescope Assets. Since details about these telescopes are not yet available to the broader astronomical community, our test case is based on a geometry mimicking the actual one, to the best of our knowledge.

The recently completed study of using one of the AFTA telescopes for a potential WFIRST mission included a coronagraph instrument for exoplanet imaging. The challenge is to design a coronagraph that achieves the desired high contrast in the presence of the complicated on-axis optical architecture of the AFTA. This is especially difficult if contrast levels as small as 10-9 must be achieved at only 3λ/D from the star. In this paper we present shaped pupil designs using our new two-dimensional formulation. These designs also include constraints given by the wavefront control system, a necessary element of a complete high-contrast system in space. We have computed various shaped pupils for different contrast floors, inner working angles, and high- contrast region shapes. Two main types of masks are presented: discovery masks that offer wide discovery space with moderate inner working angles, and characterization masks which are designed for narrower discovery space and smaller inner working angles. Discovery and characterization masks would be used to image planets at different distances from the star at the same wavelengths, or to image the same planets at different wavelengths.

Here we present two simple concepts to make the vortex coronagraph (VC) immune to heavily obscured apertures. The multi-stage VC (MSVC) uses the ability of the vortex to move light in and out of apertures through multiple VC in series to restore the nominal attenuation capability of the charge 2 vortex regardless of the aperture obscurations. The ring-apodized VC (RAVC) is a one-stage apodizer exploiting the VC Lyot-plane amplitude distribution in order to perfectly null the diffraction from any central obscuration size, and for any vortex topological charge. In this paper, we also emphasize the complementarity and similarities of the RAVC to the recently proposed Active Compensation of Aperture Discontinuities (ACAD, L. Pueyo et al. 2013, these proceedings) and more finely optimized shaped-pupil-like apodizations (A. Carlotti et al. 2013, these proceedings). This paper ends with a brief discussion about the trade-offs these techniques offer in the framework of the Extremely Large Telescopes (ELT) and the Astrophysics Focused Telescope Assets (AFTA).

We update the design, performance, and future prospects for the complex apodized Lyot coronagraph. We extend previous design work for off axis telescope with unobscured circular pupils, now to designs for high-contrast exoplanet imaging and spectroscopy with complicated pupil obscurations such as the WFIRST/AFTA telescope. Together with a pair of deformable mirrors for active wavefront control, the complex apodized Lyot coronagraph creates high contrast dark fields of view extending to within angular separations of 3 λ/D from the central star, over spectral bandwidths of 10% or more, and with throughput efficiencies greater than 35%.

A coronagraph on the Astrophysics Focused Telescope Asset (AFTA) provides a unique opportunity to conduct space based spectroscopic characterization of faint planets orbiting nearby stars. The principal components of such an instrument are the coronagraph itself, the integral field spectrograph (IFS) imager, and a wavefront control system to remove observatory instabilities and quasi-static speckles. Such a system will need to reach contrast levels between 1×10−8 and 1×10−9 at small angular separations to detect cool Jupiters and characterize exo-zodiacal light for any future flagship class missions. Here we define the two principal focal plane control laws commonly used in high contrast imaging, and perform a sensitivity study of the focal plane wavefront controllers to time varying low-order aberrations. The shortest possible timescale of these requirements is based on the time required for a Kalman filter estimator to measure the field. The integration time required to achieve adequate signal-to-noise in the estimation step is derived from the observing conditions, and the brightness of the target and its associated exo-zodiacal light. Based on this analysis we define tip-tilt and defocus stability limits, which must appear in the error budget for any low-order wavefront sensor intended for the instrument.

Thanks to the use of aspheric optics for lossless apodization, the Phase Induced Amplitude Apodization (PIAA) coronagraph offers full throughput, high contrast and small inner working angle. It is therefore ideally suited for space-based direct imaging of potentially habitable exoplanets. The PIAA concept has recently evolved to a higher performance version, the PIAA complex mask coronagraph (PIAACMC), which uses a combination of phase and amplitude focal plane mask for improved inner working angle and higher contrast. In this paper, PIAACMC design for a telescope with a large central obstruction (of size similar to AFTA’s pupil) is describe. The potential to image and study potentially habitable planets with a 2.4m telescope is considered. A PIAACMC with a 1.3 λ/D inner working angle appears particularly suitable for the telescope, thanks to a design optimization reducing sensitivity to pointing errors and stellar angular size.

The Astrophysics Focused Telescope Assets (AFTA) study in 2012-2013 included a high-contrast stellar coronagraph to complement the wide-field infrared survey (WFIRST) instrument. The idea of flying a coronagraph on this telescope was met with some skepticism because the AFTA pupil has a large central obscuration with six secondary mirror struts that impact the coronagraph sensitivity. However, several promising coronagraph concepts have emerged, and a corresponding initial instrument design has been completed. Requirements on the design include observations centered 0.6 deg off-axis, on-orbit robotic serviceability, operation in a geosynchronous orbit, and room-temperature operation (driven by the coronagraph’s deformable mirrors). We describe the instrument performance requirements, the optical design, an observational scenario, and integration times for typical detection and characterization observations.

An external occulter is a satellite employing a large screen, or starshade, that flies in formation with a spaceborne telescope to provide the starlight suppression needed for detecting and characterizing exoplanets. Among the advantages of using an occulter are the broadband allowed for characterization and the removal of light before entering the observatory, greatly relaxing the requirements on the telescope and instrument. In support of NASA's Exoplanet Exploration Program and the Technology Development for Exoplanet Missions (TDEM), we recently completed a 2 year study of the manufacturability and metrology of starshade petals. In this paper we review the results of that successful first TDEM which demonstrated an occulter petal could be built and measured to an accuracy consistent with close to 10-10 contrast. We then present the results of our second TDEM to demonstrate the next critical technology milestone: precision deployment of the central truss and petals to the necessary accuracy. We show the deployment of an existing deployable truss outfitted with four sub-scale petals and a custom designed central hub.

The external starshade is a prospective method for the direct detection and spectral characterization of terrestrial planets around other stars, a key goal identified in ASTRO2010. Validation of the numerical simulations that are critical to this approach has been challenging at very small scales (~4 cm) in the lab. We have successfully fabricated 60 cm starshades and begun a series of ground test experiments with them. We measured contrast better than 1×10-8 under challenging environmental conditions at outdoor test sites. Our experimental setup is designed to provide starshade to telescope separation and telescope aperture size that are scaled as closely as possible from the flight system. In this paper, we describe the test setup, the data acquisition, the reduction techniques, and a preliminary comparison of measured to modeled results.

An external occulter is a specially-shaped spacecraft own in formation with a telescope. It enables high-contrast imaging of the dim planetary companions of the neighboring solar system by blocking starlight before it reaches the entrance pupil. Occulters have to be designed via optimization methods that account for diffraction to most effectively block starlight. To predict occulter performance, we must verify the fidelity of the optical propagation models under scaled conditions. In this paper, we measure the contrast of a scaled occulter. The validity of the contrast calibration is determined using a baseline circular occulter. We verify contrast better than 10-10, however the measurements do not perform as well as the prediction from theoretical modelling. We attribute this difference to glint scattering off mask edges.

In conjunction with a space telescope of modest size, a starshade can be used as an external occulter to block light from a target star, enabling the detection of exoplanets in close orbits. Typically, the starshade will be placed some 50,000 km from the telescope and the system oriented so that the sun is on the opposite side of the shade to the telescope, but somewhat away from the line of sight. A small amount of sunlight can scatter from the edges of the shade directly into the telescope. Since the photon rate from an earthlike exoplanet might be only a few photons per minute, it is desirable that the scattered sunlight is also near this level. We have built an analytical model of the performance of starshade edges for both specular and Lambertian surfaces and derived requirements for properties such as reflectivity and radius of curvature. A computer model was also developed to show the appearance of the sunlight from the starshade and assess the contrast with the exoplanet. A commercial electromagnetism code was also used to investigate aspects of the results. We also constructed a scatterometer with which various test edges were measured and derived the likely performance if used in a starshade. We discuss these models and give the principal results.

Astrometry is a powerful technique to study the populations of extrasolar planets around nearby stars. It gives access to a unique parameter space and is therefore required for obtaining a comprehensive picture of the properties, abundances, and architectures of exoplanetary systems. In this review, we discuss the scientific potential, present the available techniques and instruments, and highlight a few results of astrometric planet searches, with an emphasis on observations from the ground. In particular, we discuss astrometric observations with the Very Large Telescope (VLT) Interferometer and a programme employing optical imaging with a VLT camera, both aimed at the astrometric detection of exoplanets. Finally, we set these e orts into the context of Gaia, ESA’s astrometry mission scheduled for launch in 2013, and present an outlook on the future of astrometric exoplanet detection from the ground.

NEAT is an astrometric mission proposed to ESA with the objectives of detecting Earth-like exoplanets in the habitable zone of nearby solar-type stars. In NEAT, one fundamental aspect is the capability to measure stellar centroids at the precision of 5 × 10-6 pixel.

Current state-of-the-art methods for centroid estimation have reached a precision of about 2 × 10-5 pixel at two times Nyquist sampling, this was shown at the JPL by the VESTA experiment.1 A metrology system was used to calibrate intra and inter pixel quantum efficiency variations in order to correct pixelation errors.

The European part of the NEAT consortium is building a testbed in vacuum in order to achieve 5 × 10-6
pixel precision for the centroid estimation. The goal is to provide a proof of concept for the precision requirement of the NEAT spacecraft. In this paper we present the metrology and the pseudo stellar sources sub-systems, we present a performance model and an error budget of the experiment and finally we describe the present status of the demonstration.

The NEAT (Nearby Earth Astrometric Telescope) mission is a proposition for an ESA space M-size mission within the Cosmic Vision 2015-2025 plan. The main scientific goal of the NEAT mission is to detect and characterize planetary systems in an exhaustive way down to one Earth mass in the habitable zone and further away, around nearby stars for F, G, and K spectral types. This survey would provide the actual planetary masses, the full characterization of the orbits including their inclination, for all the components of the planetary system down to that mass limit. NEAT will continue the work performed by Hipparcos and Gaia by reaching a precision that is improved by two orders of magnitude on pointed targets. We report in this paper the status of the work being carried out to technically validate NEAT.

We present and compare experimental results in high contrast imaging representing the state of the art in coronagraph and starshade technology. These experiments have been undertaken with the goal of demonstrating the capability of detecting Earth-like planets around nearby Sun-like stars. The contrast of an Earth seen in reflected light around a Sun-like star would be about 1.2 × 10−10. Several of the current candidate technologies now yield raw contrasts of 1.0 × 10−9 or better, and so should enable the detection of Earths, assuming a gain in sensitivity in post-processing of a factor of 10. We present results of coronagraph and starshade experiments conducted at visible and infrared wavelengths. Cross-sections of dark fields are directly compared as a function of field angle and bandwidth. The strength and differences of the techniques are compared.

Recent advances in coronagraph technologies for exoplanet imaging have achieved contrasts close to 1e-10 at 4 λ/D and 1e-9 at 2 λ/D in monochromatic light. A remaining technological challenge is to achieve high contrast in broadband light; a challenge that is largely limited by chromaticity of the focal plane mask. The size of a star image scales linearly with wavelength. Focal plane masks are typically the same size at all wavelengths, and must be sized for the longest wavelength in the observational band to avoid starlight leakage. However, this oversized mask blocks useful discovery space from the shorter wavelengths.

We present here the design, development, and testing of an achromatic focal plane mask based on the concept of optical filtering by a diffractive optical element (DOE). The mask consists of an array of DOE cells, the combination of which functions as a wavelength filter with any desired amplitude and phase transmission. The effective size of the mask scales nearly linearly with wavelength, and allows significant improvement in the inner working angle of the coronagraph at shorter wavelengths. The design is applicable to almost any coronagraph configuration, and enables operation in a wider band of wavelengths than would otherwise be possible. We include initial results from a laboratory demonstration of the mask with the Phase Induced Amplitude Apodization (PIAA) coronagraph.

Since 2009 the Echelle spectrograph FOCES1 is located at the laboratories of Munich University Observatories under pressure and temperature stabilized conditions. It is intended to be operated at the 2.0m Fraunhofer Telescope at the Wendelstein Observatory and it will remain under lab conditions in Munich until the telescope is fully commissioned. This has given us the unique opportunity to use FOCES as a test bed for a number of different stability issues related to high precision radial velocity spectroscopy, in particular to study spectrograph stability, illumination stability and fiber transport stability. In this paper will be presented the final optical measurement results to test temperature and pressure stabilization in the spectrograph environment with respect to simulations requirements previously published. Using measurements done by a ThAr gas discharge source, we tested the stability of our system by direct 1D spectra analysis and we verified the movement of the spot positions by changing the CCD temperature in the stabilized environment.

We have built and commissioned gas absorption cells for precision spectroscopic radial velocity measurements in the near-infrared in the H and K bands. We describe the construction and installation of three such cells filled with 13CH4, 12CH3D, and 14NH3 for the CSHELL spectrograph at the NASA Infrared Telescope Facility (IRTF). We have obtained their high-resolution laboratory Fourier Transform spectra, which can have other practical uses. We summarize the practical details involved in the construction of the three cells, and the thermal and mechanical control. In all cases, the construction of the cells is very affordable. We are carrying out a pilot survey with the 13CH4 methane gas cell on the CSHELL spectrograph at the IRTF to detect exoplanets around low mass and young stars. We discuss the current status of our survey, with the aim of photon-noise limited radial velocity precision. For adequately bright targets, we are able to probe a noise floor of 7 m/s with the gas cell with CSHELL at cassegrain focus. Our results demonstrate the feasibility of using a gas cell on the next generation of near-infrared spectrographs such as iSHELL on IRTF, iGRINS, and an upgraded NIRSPEC at Keck.

Searching for nearby habitable worlds with direct imaging and spectroscopy will require a telescope large enough to provide angular resolution and sensitivity to planets around a significant sample of stars. Segmented telescopes are a compelling option to obtain such large apertures. However, these telescope designs have a complex geometry (central obstruction, support structures, segmentation) that makes high-contrast imaging more challenging. We are developing a new high-contrast imaging testbed at STScI to provide an integrated solution for wavefront control and starlight suppression on complex aperture geometries. We present our approach for the testbed optical design, which defines the surface requirements for each mirror to minimize the amplitude-induced errors from the propagation of out-of-pupil surfaces. Our approach guarantees that the testbed will not be limited by these Fresnel propagation effects, but only by the aperture geometry. This approach involves iterations between classical ray-tracing optical design optimization, and end-to-end Fresnel propagation with wavefront control (e.g. Electric Field Conjugation / Stroke Minimization). The construction of the testbed is planned to start in late Fall 2013.